1. Field of the Invention
The present invention relates to a numerically controlled machining system (hereinafter referred to as an "NC machining system") in which a machine tool is controlled by a numerical control unit (hereinafter referred to as an "NC unit") to machine a workpiece, and more particularly to such an NC machining system having an improved system for displaying data regarding tools used.
2. Description of the Prior Art
Numerically controlled machine tools (hereinafter referred to as an "NC machine tools") are controlled by NC units which receive numerical information specifying the position of a tool with respect to a workpiece, performs an arithmetic operation based on the numerical information, and controls the tool to machine the workpiece on the basis of the results of this arithmetic operation. NC machine tools can machine workpieces into complex shapes easily with high presision at an increased rate of production.
The NC machine tool is generally constructed as shown in FIG. 1 of the accompanying drawings. The NC machine tool basically comprises an NC unit 20 for processing, through arithmetic operations, numerical information commands supplied via an input terminal 10 from an external source, and a machining unit 30 controlled by the results of the arithmetic operation effected by the NC unit 20, for machining a workpiece. The NC unit 20 is composed of an input device 21 for receiving input commands from the external source, an arithmetic unit 22 for performing arithmetic operations upon the commands from the input device 21, a memory 23 for storing the results of the arithmetic operations carried out by the arithmetic unit 22, the commands from the input device 21, and other data, a control device 24 for controlling the arithmetic operations in the arithmetic unit 22, an output device 25 for delivering the results of the arithmetic operations from the arithmetic unit 22 as outputs from the NC unit 20, and a display device 26 for displaying the contents of the memory 23 and the input information given to the input device 21. Some NC units additionally include a keyboard for inputting information into the memory 23.
The machining unit 30 has a tool 31 supported by a tool holder 32 secured to a chuck on a spindle 33 that can be rotated by a spindle motor 34 driven by signals issued from the output device 25 of the NC unit 20. The machining unit 30 includes a table 35 for securing thereon a workpiece 40 with a jig or a suitable fixture. The table 35 is movable in the direction of the X-axis by a ball screw 36 driven by an X-axis feed motor 38 through a gear box 37. The X-axis feed motor 38 is drivable under the control of signals delivered from the output device 25 of the NC unit 20. The table 35 is also movable in the directions of Y- and Z-axes by mechanisms (not shown) which are identical with the above X-axis drive mechanism and driven by signals from the NC unit 20.
When a counterbored hole 41 is to be formed in the workpiece 40 as shown in FIG. 2 by the NC machine tool of FIG. 1, the workpiece 40 is machined with a rough face mill, a fine face mill, a spot drill, a drill, and an end mill, sequentially in the order named.
This sequential machining operation will be described in more detail as illustrated in FIG. 3. As shown in FIG. 3(a), a face mill 50 is used to mill the workpiece 40 for forming a roughly flat surface, a machining step hereinafter called "rough face milling." Then, a face mill 51 which is capable of finer machining than the face mill 50 is employed to cut a fine, flatter surface; the surface formed by fine face milling being illustrated in FIG. 3(c). Thereafter, a centering hole is cut in the milled surface of the workpiece 40 by a spot drill 52, as shown in FIG. 3(d). This machining step is called "spot drilling" in which a bore is formed in the workpiece 40 by a drill 53, as shown in FIG. 3(e). Then, an end mill 54 is used to enlarge the bore at its end with a square shoulder at the enlarged end, thereby forming a counterbored hole 41, as illustrated in FIG. 3(f). The final machining step is called "end milling."
FIG. 4 shows the fundamental construction of a machining program enabling the NC machine tool to effect the counterboring operation as described in FIGS. 2 and 3. The machining program is composed of machining pattern specifying blocks, tool specifying blocks, and positional information specifying blocks. Each machining pattern specifying block serves to specify a machining pattern such, for example, as counterboring, threading, or boring. As is apparent from the counterboring operation shown in FIG. 3, a plurality of tool specifying blocks and a plurality of positional information specifying blocks are normally required. Each tool specifying block is used for specifying a tool for a particular machining operation, and the following positional information specifying block serves to specify positional information for machining with the specified tool. The machining program is written on a coding sheet outside the NC unit 20 and punched onto a paper tape. There is provided a means for reading the punched program and loading the same into the NC unit through the input terminal 10 (FIG. 1) to effect the machining operation, or a means for fully storing the punched program into the memory 23 (FIG. 1) and reading the program out of the memory to perform the machining operation. Alternatively, an NC unit with provision for creating a machining program may be employed, and a machining program may be stored directly in the memory through a control panel of the NC unit such as a keyboard, the stored program being successively read for carrying out the machining operation.
A method of creating a machining program will be described in detail with reference to FIG. 5. FIG. 5(a) is a flowchart for preparing a machining program, and FIG. 5(b) is illustrative of the prepared machining program. For creating a machining program, a machining pattern such as a counterbore as shown in FIG. 2 is given as a command. Then, a command is prepared for returning the workpiece supporting table in the NC machine tool to a reference point along the X-, Y-, and Z-axes. Then, a command for the first tool to be used is prepared, the tool command being normally expressed by a "T" number. For a program for forming the counterbore of FIG. 2, a command is prepared for specifying the rough face mill as shown in FIG. 3(a). The next step is to create a command for moving the tool to a machining starting point. Subsequently, a command for rotating the spindle with the tool mounted thereon, a command for specifying the speed of rotation of the spindle, and a command for specifying the cutting path and machining speed are successively prepared to enable the tool to machine the workpiece to a predetermined shape under these commands. Then, a command for stopping the rotation of the spindle is created. With this stopping command, the machining operation using the specified tool is brought to an end. Thereafter, a command for specifying the next tool is created. In case the counterbored hole as illustrated in FIG. 2 is to be formed, the face mill with higher machining accuracy as shown in FIG. 3(b) is specified by this tool specifying command. Then, the commands 4 through 8 are prepared again to set up the machining mode using the second tool. Machining modes for respective tools used are prepared in the foregoing manner until a desired machining program is completed.
Under the machining program thus prepared, a plurality of tools are employed and mounted on an automatic tool changer provided in the NC machine tool. The automatic tool changer is effective to automatically change tools on the spindle under tool commands. The automatic tool changer has a tool magazine for holding a number of tools, the tool magazine including tool pockets marked with pocket numbers (PK NO) which are the same as tool commands "T". Prior to any machining operation based on a desired machining program such as shown in FIG. 5, the operator is required to place tools required by the program in the tool pockets with the pocket numbers corresponding respectively to the "T" numbers according to the machining program.
One prior tool attachment practice is for the machining program as illustrated in FIG. 5(b) to be all displayed on the display 26 in the NC unit. Where the display 26 is in the form of a cathode-ray tube (CRT), the machining program for forming the counterbore as shown in FIG. 2 is displayed in a pattern as shown in FIG. 6. The CRT 26 displays on its screen all of the machining program including the tool commands T1053, T1054, T1055, T1045, T1044, T1046, and the machining modes using the specified tools. The operator prepares and sets tools with reference to a referance table wherein the T numbers and the tools are listed in 1-to-1 correspondence according to the displayed program. As an example, the reference table enables the operator to identify "T1053" as a "rough face mill".
Since the tools are identified simply as symbols such as T numbers in the displayed program, the operator has to refer to the reference table to select or prepare desired tools, and thus the tool selection procedure is troublesome.
The prior NC machining system is also disadvantageous in that the CRT 26 also displays many numbers and symbols unnecessary for tool selection, and the operator finds it tedious and time-consuming to locate only the "T" numbers in the displayed machining program. Therefore, a long period of time has been needed for preparing the necessary tools. For tool preparation, only tool commands 3 and 8 in the program as shown in FIG. 5 are needed, and other data items expressed in numbers and symbols are unnecessary.